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IC 9222 



BUREAU OF MINES 
INFORMATION CIRCULAR/1989 

"D 



Position and Heading Determination of 
a Continuous Mining Machine Using 
an Angular Position-Sensing System 



By Donna L. Anderson 



o?" 



imdu* 



UNITED STATES DEPARTMENT OF THE INTERIOR 

i 



Mission: As the Nation's principal conservation 
agency, the Department of the Interior has respon- 
sibility for most of our nationally-owned public 
lands and natural and cultural resources. This 
includes fostering wise use of our land and water 
resources, protecting our fish and wildlife, pre- 
serving the environmental and cultural values of 
our national parks and historical places, and pro- 
viding for the enjoyment of life through outdoor 
recreation. The Department assesses our energy 
and mineral resources and works to assure that 
their development is in the best interests of all 
our people. The Department also promotes the 
goals of the Take Pride in America campaign by 
encouraging stewardship and citizen responsibil- 
ity for the public lands and promoting citizen par- 
ticipation in their care. The Department also has 
a major responsibility for American Indian reser- 
vation communities and for people who live in 
Island Territories under U.S. Administration. 



Information Circular 9222 

ii 



Position and Heading Determination of 
a Continuous Mining Machine Using 
an Angular Position-Sensing System 



By Donna L. Anderson 



UNITED STATES DEPARTMENT OF THE INTERIOR 
Manuel J. Lujan, Jr., Secretary 

BUREAU OF MINES 
T S Ary, Director 



T^ MS* 





* 



Library of Congress Cataloging in Publication Data: 



Anderson, Donna L. 

Position and heading determination of a continuous mining machine using an 
angular position-sensing system. 

(Bureau of Mines .information circular; 9222) 

Supt. of Docs, no.: I 28.27:9222. 

1. Mining machinery-Automatic control-Data processing. 2. Lasers in mining. 
I. Title. II. Series: Information circular (United States. Bureau of Mines); 9222. 



TN295.U4 



[TN345] 



622 s [622'.028] 



89-600000 



CONTENTS 

Page 

Abstract 1 

Introduction 2 

Sensory system 3 

Computer interface 4 

Position determination using angular position data 4 

Sensor fusion algorithm 7 

Conclusions 8 

ILLUSTRATIONS 

1. Cutting sequences for straight cut 2 

2. Cutting sequences for crosscut 2 

3. Continuous miner advancing face under MCS 3 

4. Angular position of two same targets on continuous miner from two Lasernet units on MCS 5 

5. Two triangles formed by representing position of each target as vertex of triangle, and separation 

between lasers as length of baseline 5 

6. Angular position of three targets on continuous miner from one Lasernet unit on MCS 6 

7. Three triangles formed by representing Lasernet unit's position as common vertex, and targets 

separations as baselines of triangles 7 



UNIT OF MEASURE ABBREVIATION USED IN THIS REPORT 

ft foot 



POSITION AND HEADING DETERMINATION OF 
A CONTINUOUS MINING MACHINE USING 
AN ANGULAR POSITION-SENSING SYSTEM 



By DONNA L. ANDERSON 1 



ABSTRACT 

This U.S. Bureau of Mines report describes a system to determine the position and heading of a 
continuous mining machine during the maneuvers required at the face area of a mine. The system 
consists of commercially available angular position sensors and a computer interface developed and 
tested at the Bureau. The sensors employed are laser-based scanning devices that report the angular 
location of retroreflective targets within their 90° field-of-view. The targets are mounted on the 
continuous mining machine; the laser scanners are mounted on an external reference structure. The 
computer interface consists of a single-board computer-controller programmed to gather and process 
the angular position information, and to calculate the machine's position and heading relative to the 
reference structure. A sensor fusion algorithm will be incorporated into the computer interface 
programming to increase the accuracy and reliability of the system. 



Electrical engineer, Pittsburgh Research Center, U.S. Bureau of Mines, Pittsburgh, PA. 



INTRODUCTION 



The purpose of a position and heading determination 
system for a continuous miner is to provide the informa- 
tion necessary for automated navigation at the face. 
Autonomous face navigation is a crucial step towards auto- 
mating face operations, which will result in an increase in 
the safety and productivity of current mining operations. 
A brief description of the overall autonomous face naviga- 
tion scheme will serve to illustrate the role of this position 
and heading determination system. 

The navigation of a continuous mining machine at the 
face consists of the task of controlling the position and 
heading of the continuous miner during the cutting process 
so that coal is removed according to the mine plan. The 
guidance for a two-pass continuous mining machine per- 
forming straight cuts and crosscuts in room-and-pillar 
mining is the focus of this research. The cutting sequences 
are shown in figures 1 and 2. This task requires that the 
continuous miner be provided with a reference indicating 



the position and heading of the desired cut, along with a 
method to determine the position and heading of the con- 
tinuous mining machine with respect to the reference. 

A mobile control structure (MCS) will be employed as 
a reference for guidance in the face area. The MCS, cur- 
rently being designed at the Bureau of Mines, will serve 
as a control center for face operations in a mine. It will 
be precisely positioned in the face area, serving as a phys- 
ical indication of both the position and heading of the de- 
sired cut and thereby providing a fixed, stable reference 
to guide all face navigation. 

As the continuous mining machine maneuvers under- 
neath the MCS (fig. 3), it will refer to the position of the 
MCS as a reference for alignment. During the cutting 
process, the continuous miner will continue to update its 
position and heading relative to the reference. After a full 
straight cut is completed, i.e., when the face has been ad- 
vanced 20 ft, the MCS will automatically advance 20 ft in 




" win irinlii 




Figure 1. -Cutting sequences for straight cut. 



Figure 2. -Cutting sequences for crosscut 




Figure 3.-Continuous miner advancing face under MCS. 



the entry. It will use the position of the now stationary 
continuous mining machine as a reference, thereby 
maintaining a constant heading to guide the next cut. The 
MCS will also have the maneuverability to negotiate a 
corner and provide the reference for guidance after a 
crosscut has been started. 



The following is a description of a working system 
composed of a sensory system and computer interface, 
which obtain and process the information necessary to 
determine the relative position and heading of the MCS 
and continuous miner. 



SENSORY SYSTEM 



Lasernet, 2 a laser-based optical scanning device devel- 
oped by Namco Controls, Mentor, OH, will be employed 
to obtain the navigational information. This device is ca- 
pable of determining the angular position of special retro- 
reflective targets located in its planar and angular field-of- 
view. Multiple laser-scanning units will be mounted on the 



Reference to specific products does not imply endorsement by the 
U.S. Bureau of Mines. 



MCS, and multiple targets will be mounted on the contin- 
uous mining machine. In this configuration, the more 
fragile laser-scanning units will experience less shock and 
vibration, thus prolonging their life and maintaining 
greater accuracy. A data link will provide both the con- 
tinuous miner and the MCS the information necessary to 
determine their position and heading relative to the de- 
sired cut for alignment and guidance at the face. 



Lasernet is an industrial sensor designed to provide 
navigational information to automated guided vehicles on 
a factory floor. It uses a Class II helium-neon laser light 
source, which produces a visible red light beam. The 
beam is directed at a rotating mirror, which sweeps a 
horizontal beam of laser light across a 90° field-of-view at 
a constant angular velocity. At the start of each scan, 
Lasernet stores the value of an internal free running 
counter. When the beam encounters special retroreflective 
targets, a pulse of light is reflected back to the unit and 
detected by a photodetector. The value of the counter is 
again recorded at the time of reception of the leading and 
trailing edges of the pulse. The counts are processed upon 
completion of a scan. 

Lasernet offers various options for processing the 
counter information. For this application, it has been 
configured to take the leading and trailing edge counts, 
determine the count to the center of the target, and deliver 
a raw angle count (RAC) corresponding to the number of 
counts from the start of the scan to the center of the 
target. Upon request, the RAC's are delivered out the 



serial line. These values are proportional to the angular 
position of the center of the targets. For a 90° field-of- 
view, the maximum angle count is 15,360, or 170.666 
counts per degree. Therefore, the angular position in 
degrees relative to the center of the field-of-view of the 
Lasernet is determined from the following formula: 

Angle (degree) = [(90/15360) * RAC] - 45° 

Lasernet is also configured to compare the counts at the 
start of each scan to determine the motor scan velocity. A 
speed tolerance is set, and it will not process any target 
edge data that have been read when the motor scan veloc- 
ity error exceeds that tolerable limit. Therefore, any bad 
data taken when the unit experiences shock or vibration 
can be ignored. Also, Lasernet is configured in a multiple 
target mode in which it will process the information for up 
to eight targets during each scan. Multiple target informa- 
tion is necessary to determine the heading of the MCS- 
continuous miner. 



COMPUTER INTERFACE 



The computer interface consists of a BCC52 computer- 
controller and three BCC08 serial expansion boards, 
developed by Micromint, Inc., Vernon, CT. The BCC52 
is a stand-alone single-board computer programmable in 
the BASIC-52 or MCS-51 assembly languages. It has been 
programmed to gather and process the RAC's from the 
Lasernet units, and to calculate the position and heading 
of the continuous mining machine. The three BCC08 
serial expansion boards permit RS-232 communications 
with up to three Lasernet units. 

The interface has been designed to operate in a flexible 
system consisting of one, two, or three Lasernet units. 
Therefore, each serial connection is tested to verify the 
presence of a working unit. A control byte is then 
delivered to each unit to set the options for processing the 
counter information (i.e., center target request, speed 
tolerance, and multiple target mode). The RAC's are 
requested. Once all units have been polled, and their 
counts received, the counts are converted to degrees, and 
this information is passed to two routines for position 
determination. 

POSITION DETERMINATION USING 
ANGULAR POSITION DATA 

The first routine will calculate the position and heading 
of the continuous miner given the angular position of two 
same targets of known position on the continuous miner 
relative to two Lasernet units. The second routine can do 
the same given the angular position of three targets 
relative to one Lasernet unit. 

Figure 4 illustrates the first situation. The angular 
position of two same targets (A,B) from two Lasernet 



units (L1,L2) is given. The separation between the laser- 
scanning devices represents the length of the baseline, and 
each target position represents the vertex of a triangle 
(fig. 5). Since the separation between laser devices (d 12 ) 
is known, and the angles to the targets (9 A1 9^ and 9 B1 
9 B2 ) are given from the Lasernet data, the length of the 
side (d A1 d B1 ) can be determined. 
By using the law of sines 



J A1 



d 12 



sin (9^) sin (180 - 9 A1 - 9^) 



and 



J B1 



'12 



sin (9 B2 ) sin (180 - 9 B1 - 9 B2 ) 



The position of each target relative to LI can then be 
determined by projecting the sides of the triangles onto the 
x and y axis, 



x A = d A1 sin(9 A1 ) 



V A = d Al C0S ( e Al) 



Xd = 



d B1 sin (9 B1 ) 



y B = d B1 cos (9 B1 ). 



Finally, the heading (h) of the targets relative to the 
centerline of the cut (y axis) can be calculated from the 
two positions, 



tan 



V A- V B 




Figure 4. -Angular position of two same targets (A,B) on 
continuous miner from two Lasernet units (L1,L2) on MCS. 



Figure 6 demonstrates the second situation. The angu- 
lar position of three targets (D, E, F) relative to one laser 
scanning device (L3) is given. Three triangles are formed 
by representing the position of L3 as a common vertex, 




AU A ,Y A ) 




■>X 



Figure 5.-Two triangles formed by representing position of 
each target as vertex of triangle, and separation between lasers 
as length of baseline. 



and the various target separations as the baselines of the 
triangles (fig. 7). These triangles share some common 
angles and sides, and provide the following three equations 
with three unknown values. 
By using the law of sines, 



*E 



•TE 



sin (Oj) sin (0 F - 6 E ) 



and 



l E 



a ED 



sin (9 2 ) sin (6 E - 6 D ) 
By using the sum of angles law 

180 = (e F - g d ) + e x + e 2 . 



By equating first and second equations, a relationship 
between Gj and 6 2 is found. The values of these angles 
can then be determined by substituting in the third equa- 
tion. The following two equations result: 



tan 



-l 



sin K, 



.(K x / K 2 ) + cos K^ 



where 



and 



*1 


sin (9 F - Gg) 


K, 


d ED 


^2 


sin (9 E - 9 D ) 


K 3 


= 180 - e F - e D . 



9 2 = tan 



-1 



sin K, 



_(K 2 / KJ + cos % 



The sides of the triangles (sensor-to-target distances) 
can then be calculated by using the law of sines, as shown 
in the following equations: 



'FD 




Figure 6. -Angular position of three targets (D,E,F) on 
continuous miner from one Lasemet unit (L3) on MCS. 



and 



-D 


sin (6p - 


9 D ) 


dr~ = 


d ED 




U E 


sin (9 E ■ 


e D ) 


dr^ " 


d FD 




Up 


sin (9 F - 


e D ) 



x sin 9 



1 » 



x sin 9 



2> 



x sin 9 2 



As shown in the first routine, the position of each target 
relative to L3 can be determined by projecting the sides of 
the triangles onto the x and y axis. The heading (h) of the 




e F -e 



8 f -8 E 



Figure 7.-Three triangles formed by representing Lasernet 
unit's position as common vertex, and targets separations as 
baselines of triangles. 



targets relative to the centerline of the cut can then be 
calculated from two target positions. 

These two routines demonstrate the minimum angular 
position information necessary to determine position and 
heading. Either the angular position of two same targets 
from two Lasernet units or the angular position of three 
targets relative to one Lasernet unit is necessary. How- 
ever, the current system is configured to support as many 
as three Lasernet units and five targets. The accuracy and 
reliability of this system are increased as more Lasernet 
units and more targets are added to the system. If any 
Lasernet unit fails, or target goes out of view, other lasers 
and targets will continue to provide adequate guidance 
information, thus increasing the reliability of the system. 
Additionally, at times when more than the minimum infor- 
mation is available, a sensor fusion algorithm which fuses 
all the gathered data together can provide a more accurate 
determination of position and heading. 

SENSOR FUSION ALGORITHM 

The current system (three lasers, five targets) will most 
often provide a redundant source of position and heading 
information. The accuracy of the position and heading 
determination can be increased by assigning weights (W) 
to the values obtained from the laser system and averaging 
the combined information. 

Each of the position and heading values 
[V(l),V(2),V(3)...V(n)] can be assigned a confidence level 
[C(l),C(2),C(3)...C(n)]. The confidence levels represent 
the accuracy and reliability of the laser system and are 
determined from prior experiments and analysis. These 
experiments and analysis will indicate times and conditions 
under which the data are accurate and reliable. 

Experiments are currently being conducted to determine 
the inherent accuracy of Lasernet. These tests will deter- 
mine Lasernet's angular position accuracy with respect to 
the target's range and angular position. An irregularity in 
the scanning motor is one possible source of inherent 
error. 

Aside from the inaccuracies inherent in the Lasernet 
unit, other analysis will provide information leading to the 
determination of confidence levels. It will determine rel- 
evant information such as the relationship between the 
angular separation between targets and the accuracy of the 
angular report. Also, it will determine the effect of certain 
geometric orientations of targets and lasers that affect 
angular accuracy. For example, a line of targets approach- 
ing a perpendicular orientation relative to the laser radial 



will result in a less reliable calculation of position and 
heading, and targets approaching a parallel orientation will 
result in an indeterminate situation. Additionally, environ- 
mental factors that affect accuracies of Lasernet's angular 
report, such as dust or water, will be evaluated. All this 
information will be used to predict the confidence of 
Lasernet's data. 

Once all experiments and analyses are complete, the 
expected performance of Lasernet will be known. The 
confidence of one laser unit may be determined from the 
data from other units. This situation may arise when the 
data from one or a few laser units can be used to deter- 
mine that another laser unit is operating outside its accu- 
rate range. The confidence level can then be lowered 
according to the results of the prior experiments. In 
another case, the confidence will be affected by a dust 
sensor on the machine that indicates a high concentration 
of dust. Again, the results of the dust performance tests 
will be used to predict the confidence of the data. 

Once a confidence level is determined for the data, 
average weights (W) can be calculated from the percent- 
age confidence levels. 

W(i) = C(i) / [C(l) + C(2) + ... + C(n)] 

The fused value V(f) of position and heading is then 
determined by 

V(f) = W(l) * V(l) + W(2) 



* V(2) + ... + W(n) * V(n) 

This value is the position and heading of the targets on 
the continuous miner relative to Lasernet units on the 
MCS. The target positions on the continuous miner and 
the Lasernet positions and orientations on the MCS are 
known; therefore, the relative position and heading of the 
continuous miner and MCS can be determined. At times 
when the continuous miner is using the MCS as a refer- 
ence, the orientation of the MCS with respect to the 
desired cut is known, therefore the continuous miner's 
position and heading relative to the desired cut can be 
determined. At times when the MCS is guiding from the 
targets on the continuous miner, the continuous miner's 
position and heading with respect to the desired cut are 
known, and the position and heading of the MCS with 
respect to the desired cut can be determined. 



CONCLUSIONS 



A method for position and heading determination to 
provide feedback for guidance of a continuous mining 
machine through the maneuvers required at the face area 
of a mine was described. It incorporated a commercially 
available angular position sensing system with a computer 
interface developed and tested at the Bureau. 

The current system consists of up to three laser-based 
optical scanning units which report the angular location of 
five retroreflective targets within their 90° field-of-view. 



The computer interface gathers the data from the Lasernet 
units, converts them into usable units, and employs two 
trigonometric routines to calculate the position and head- 
ing of the continuous miner. Experiments are currently 
being conducted to determine the expected performance 
of Lasernet. A sensor fusion algorithm that will use these 
data has been outlined and will be incorporated into the 
interface programming to increase the accuracy and 
reliability of the system. 



* U.S. GOVERNMENT PRINTING OFFICE: 611-012/00,082 



INT.BU.OF MINES.PGH..PA 28920 



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